1. Field of the Invention
The invention relates to microwave radio frequency transmission line circuits generally, and more specifically to four-port hybrids instrumented in stripline, microstrip, and the like.
2. Description of the Prior Art
The so-called hybrid is per se well known and well understood in this art in its waveguide, coaxial and stripline forms. These devices serve as power-dividing, summing, and differencing networks and are widely used in microwave systems. In the text Radar Handbook by Merrill I. Skolnik (McGraw-Hill Book Company 1970), the general class of devices called "microwave junctions" (which includes the so-called hybrid) is described in its prior art forms.
Immediately before that description, the Skolnik handbook discusses stripline and microstrip transmission lines, and it is in media of that type that the invention to be described hereinafter has been implemented. Other technical references describe the stripline, microstrip and similar transmission lines structures, such as Antenna Engineering Handbook, Henry Jasik, editor, McGraw-Hill 1961 (First Edition).
A basic element employed in the combination of the invention is described as an "all-pass filter" in the paper "Coupled-Strip-Transmission-Line Filters and Directional Couplers" by E. M. T. Jones and J. T. Bolljahn (IRE Transactions on Microwave Theory and Techniques, April 1956). In that paper, the basic design criteria for various coupled-strip configurations are given in physical dimension and impedance relationships. The so-called "all-pass" filter included in the Jones and Bolljahn description will be recognized as an inherently broadband device.
In a technical paper by B. M. Schiffman ("Transactions on Microwave Theory and Techniques"--IEEE April 1958), an application of the coupled-strip elements to produce a 90.degree. phase shifter is described.
The typical prior art hybrid is in the 11/2 wavelength hybrid ring, as shown in FIG. 16 (page 8-17) of the aforementioned Radar Handbook, that form being adapted for instrumentation in stripline or microstrip. This prior art hybrid ring is effective for narrow frequency bandwidths, or in applications wherein variations with frequency is isolation, power division, and phase characteristics can be tolerated, although its geometry inherently makes it less compact and less convenient for inclusion in microwave circuitry than that according to the invention hereinafter described.
A prior copending United States Patent Application by the same inventor entitled "Broad-Band Printed-Circuit Balun," Ser. No. 443,419, filed Nov. 22, 1982, now U.S. Pat. No. 4,460,877 issued July 17, 1984, discloses a printed circuit balun which, like the herein described hybrid, is implementable in stripline, microstrip, or the like. The aforementioned balun invention also makes use of coupled-strip, all-pass, printed circuit filter sections as described by Jones et al. and Schiffman (identified hereinbefore). That patent application is assigned to the assignee of this application and the inventorship is the same. The disclosure of that application (Ser. No. 443,419) is incorporated herein by reference.
The manner in which the invention advances the state of this art will be evident as this description proceeds.